New system protocols like LTE require additional antennas in mobile phones. In order to perform adequately, every antenna in a mobile phone requires a dedicated volume which is sufficiently free from other components. In addition to this, the more antennas a mobile phone occupies, the more difficult it will be to ensure the interoperability of these antennas. Therefore, there is a need to reduce the number of antennas in a mobile phone.
Apart from the cellular antennas, a mobile phone typically comprises a variety of antennas including antennas dedicated for a wireless local area network (WLAN) and/or BlueTooth. Typically, mobile phones have separate cellular antennas and a WLAN/BlueTooth antenna. Cellular antennas are typically variants of inverted F-antennas or inverted L-antennas, implemented on normal plastic carriers using either flex-film assembly or laser-direct structuring. Alternatively, the antennas can be directly implemented into the phone mechanics, e.g., with flex-film assembly. Typical WLAN/BlueTooth antennas are implemented either as ceramic chip antennas or similarly as above-described cellular antennas. WLAN/BlueTooth antennas can also be implemented on the same plastic carrier as cellular antennas. A common challenge experienced in this implementation is the isolation between cellular and WLAN/BlueTooth antennas, where a typical target can be 10 dB of isolation between the antennas. From a co-existence point of view, LTE band 7 is most problematic because of the close proximity of band 7 TX and RX frequencies to WLAN frequencies. Here, it is challenging to provide sufficient isolation between the antennas. Filtering is also difficult due to limited selectivity of filters.